1. Field of the Invention
The present invention relates to a method for dispersing carbon nanotubes (CNT), and particularly in an aqueous solution. The present invention also relates to a dispersion obtained via this method, which serves as an agent for calibrating concentration of carbon nanotubes.
2. Related Prior Arts
Conventionally, to reinforce mechanical strength, thermal stability and durability of plastic material, additives such as ceramics, metal, carbon fibers, active carbon, etc., are added therein. However, it's difficult to well disperse the additives in plastic. As a novel material with superior characteristics, carbon nanotubes are widely applied to processing of various industries. However, it's still a problem to disperse the carbon nanotubes in a matrix.
Due to the curled graphite structure, lots of resonant it electrons and huge molecular weight, the carbon nanotubes are hardly soluble in water or other organic solvents. In some reports as follows, surfactants, organic solvents, strong acids, strong base and high temperature are applied to promoting dispersion of the carbon nanotubes.    (1) Amphoteric polymeric surfactant: the dispersion can last four days. (Vladimir A. Sinani, Muhammed K. Gheith, Alexander A. Yaroslavov, Anna A. Rakhnyanskaya, Kai Sun,| Arif A. Mamedov, James P. Wicksted, and Nicholas A. Kotov, Aqueous Dispersions of Single-wall and Multiwall Carbon Nanotubes with Designed Amphiphilic Polycations J. AM. CHEM. SOC. 2005, 127, 3463-3472)    (2) Poly(4-vinylpyridine) (P4VP): the CNT/alcohol dispersion can last 1˜6 weeks. (Jason H. Rouse Polymer-Assisted Dispersion of Single-Walled Carbon Nanotubes in Alcohols and Applicability toward Carbon Nanotube/Sol-Gel Composite Formation, Langmuir 2005, 21, 1055-1061)    (3) Tank-type ultrasonic oscillator: the CNT/water dispersion can last only 5 minutes. (Yangchuan Xing, Liang Li, Charles C. Chusuei, and Robert V. Hull, Sonochemical Oxidation of Multiwalled Carbon Nanotubes, Langmuir 2005, 21, 4185-4190)    (4) Porphyrin: time for lasting the dispersion is not mentioned. (Jinyu Chen and C. Patrick Collier Noncovalent Functionalization of Single-Walled Carbon Nanotubes with Water-Soluble Porphyrins, J. Phys. Chem. B, Vol. 109, No. 16, 2005 7605-7609)    (5) Reductive metal such as Li and Na: the dispersions of CNT in organic solvents (such as THF, DMF, DMSO) can be quickly achieved but have to be preserved in nitrogen, and Li and Na are uneasily preserved. (Alain Pe'nicaud, Philippe Poulin, Alain Derre', Eric Anglaret and Pierre Petit, Spontaneous Dissolution of a Single-Wall Carbon Nanotube Salt, J. Am. Chem. Soc.; 2005; 127; 8-9)    (6) Ionic aromatic: time for lasting the dispersion is not mentioned, and the ionic aromatic is difficulty synthesized and possibly carcinogenic. (Hanna Paloniemi, Taina Laiho, Hanna Liuke, Natalia Kocharova, Keijo Haapakka, Fabio Terzi, Renato Seeber, and Jukka Lukkari, Water-Soluble Full-Length Single-Wall Carbon Nanotube Polyelectrolytes: Preparation and Characterization, J. Phys. Chem. B 2005, 109, 8634-8642)
According to the above reports, it's desired to develop a technology of dispersing the carbon nanotubes in a solution without the above problems.